The present invention relates to vehicle coefficients of force being offset through suspension damping, and, in particular, to a method and system for providing slew rate limiting parameters for use with suspension damping control outputs.
Known variable force suspension systems include variable force shock absorbers and/or struts that provide suspension damping forces at a magnitude controllable in response to commands provided by a suspension system controller. Some systems provide control between two damping states and others provide continuously variable control of damping force.
In a known manner of control of a variable force suspension, the demand force for each variable force damper is determined responsive to a set of gains, the wheel vertical velocity and the body heave, roll and pitch velocities. An example system determines the demand force as follows: DFb=GhHxe2x80x2+G,Rxe2x80x2+GpPxe2x80x2+Gwxcexd, where DFb is the demand force, Gh is the heave gain, Gr is the roll gain, Gp is the pitch gain, Gw is the wheel velocity gain, Hxe2x80x2 is the body heave velocity, Rxe2x80x2 is the body roll velocity, Pxe2x80x2 is the body pitch velocity and xcexd is the wheel vertical velocity. The portion of the demand force computation GhHxe2x80x2+G,Rxe2x80x2+GpPxe2x80x2, represents the body component determined responsive to the body heave, roll, and pitch velocities. The portion of the demand force computation Gwxcexd represents the wheel component determined responsive to the difference between the computed body corner velocity and the body-wheel relative velocity.
A control signal representing the determined demand force is output to control the variable force damper responsive to the demand force. Example systems are described in U.S. Pat. Nos. 5,606,503; 5,235,529; 5,096,219; 5,071,157; 5,062,657; and 5,062,658. Current damping algorithms tend to change the damper output signals abruptly during zero crossings of the associated damper relative velocity signal. Over large inputs, which cause significant body motions, it is sometimes more desirable to retain an elevated damping state. Damper output stewing is a means known in the art for performing this function, however its slew rate parameters cause excess damping control to be present during normal driving. The excess damping causes unwanted forces to be dissipated throughout the vehicle.
Therefore, it would be desirable to have an algorithm that would mode or switch the slew rate limiting parameters in order to allow longer slew times during large inputs and smaller slew times during smaller inputs. Such an algorithm would provide for smoother, more complete control over large inputs caused by rough terrain, while not adversely affecting ride comfort over other road surfaces.
One aspect of the invention provides a method for controlling dampers in a suspension system of a vehicle body. A heave velocity of a vehicle body is derived from sensed dynamic variables of the vehicle body. A slew rate limit for a damping control command is derived in response to the heave velocity of the vehicle body. The damping control command for at least one dampers is generated in accordance with the slew rate limit. The limited damping control command is applied to the at least one damper.
Another aspect of the invention provides a method of determining a slew rate limit for a suspension damping control system. An average heave velocity is determined. The slew rate limit is then determined as a function of the average heave velocity.
Another aspect of the invention provides a control module for a suspension damping control system comprising a means for deriving a heave velocity of a vehicle body from sensed dynamic variables of the vehicle body, a means for deriving a slew rate limit for a damping control command in response to the heave velocity of the vehicle body, a means for generating the damping control command for at least one dampers in accordance with the slew rate limit, and a means for applying the limited damping control command to the at least one damper.
Another aspect of the invention provides a control module for a suspension damping control system comprising means for determining an average heave velocity; and means for determining a slew rate limit as a function of the average heave velocity. Another aspect of the invention provides a computer readable medium storing a computer program comprising computer readable code for deriving a heave velocity of a vehicle body from sensed dynamic variables of the vehicle body, computer readable code for deriving a slew rate limit for a damping control command in response to the heave velocity of the vehicle body, and computer readable code for generating the damping control command for at least one dampers in accordance with the slew rate limit.
Another aspect of the invention provides a computer readable medium storing a computer program comprising computer readable code for determining an average heave velocity, and computer readable code for determining a slew rate limit as a function of the average heave velocity.
The invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof.